High-volume printers are increasingly used in production of large print jobs, such as book printings or mass mailings. These printers typically are driven by a printer controller and include a print engine that controls a group of printheads that produce printed pages. The print engine also typically includes a print engine buffer to store pages until they can be printed. Some of these high-volume printers, such as some industrial inkjet printers manufactured by Miyakoshi Printing Machinery Co. and others, are variable speed printers that have variable speed print engines that modify the printing speed based on the number of pages in their buffer. Variable-speed printers provide additional flexibility over fixed speed printers, but the variable-speed feature can cause problems when speeds drop too low or when print loads fluctuate.
Print engines for variable speed printers usually have a multi-page buffer of pages to be printed. If the buffer is full, the print engine increases the speed of the printer to the maximum allowable speed. As the buffer empties, the print engine may decrease the speed. If the print engine ever allows the buffer to completely empty and thus runs out of print data to be printed, the printer must print blank pages. Printing blank pages results in paper waste and makes post-processing more difficult and expensive. Post-processing is more difficult as the blank pages need to be removed from the print job either manually or by automated process, both of which result in additional time and expense. This problem is exacerbated for color printheads, such as Cyan Magenta Yellow blacK (CMYK) printheads, where colors are laid down sequentially and a back side may also need to be printed for each page, as well as any printer with multiple printheads.
Some print engines try to solve this problem by beginning to slow down the printer when pages suddenly decrease in availability, such as when the job performance suddenly drops. At times, this drop will occur faster than the print engine can slow down the printer, resulting in an underrun occurring and printing blank pages until the printer is stopped. Large high-volume printers are typically difficult to slow down quickly as they have a large amount of momentum. Even if the momentum problem can be overcome and they physically can be slowed quickly, drastic changes in printer speed can result in additional printing problems. If the speed of a printer changes too quickly, the alignment of the pages between different printheads can be skewed, resulting in blurriness or lengthening or contracting of the printed image. For a CMYK printer, for example, the printer will likely be required to be slowed gradually, as each page must go through the color printheads and possibly a dryer (and possibly for both sides of the paper), making the rate of deceleration even slower. Very strong deceleration may also result in tearing of the roll of paper, requiring the production line to be stopped and the paper reloaded, and resulting in wasted resources of time and materials.
Another solution to this problem is to increase the size of the print engine buffer. This, however, increases the cost of the print engine and serves no other benefit than to better regulate print speed. Such increased print engine buffer is also effectively wasted when smaller or less difficult print jobs are run. Additionally, the print engine buffer is integral to the print engine and thus must be purchased with the print engine itself at a time when printing needs may not yet be fully known.
Another solution to this problem is to provide a manual speed selection on the print engine that allows an operator to manually select the speed at which a print engine will run a particular job. This would require the cooperation of the print engine manufacturer and the printer owner or print controller manufacturer may not have a sufficient business case to ask for special considerations from the print engine manufacturer (i.e., their needs are too small). Moreover, the operator would have to estimate the appropriate speed setting depending on the length and complexity of the job and could underestimate or overestimate the appropriate speed. This would result in either underruns or failures to utilize the best possible speed of the printer.
There is, therefore, a need for an effective and efficient system to manage the print speed of a variable speed printer. There is an even greater need for such a system when the print jobs the printer is used for vary significantly in length or complexity.